This invention relates to a continuously variable toroidal transmission.
A continuously variable toroidal transmission (C.V.T. or variator) usually has input and output discs situated coaxially relative to a common shaft, arranged in pairs and having toroidal inner surfaces, and wheels placed between the toroidal forming pairs of input and output discs. The wheels are in frictional contact both with the input discs and the output discs and by frictional contact transmit torque transmitted to them by the input disc to the output disc, the speed of the toroidal wheels being higher the larger the space between their point of contact with the input disc and the axis of rotation. The speed of the output discs, on the other hand, is higher the closer the point of contact between toroidal wheel and output disc to the axis of rotation. Accordingly, by tilting the toroidal wheels, it is possible continuously variably to adjust at will the speed of the output disc. For this purpose, the axes of rotation of the toroidal wheels are placed on a support which can be controlled by a swiveling device.
The basic principle of such a continuously variable toroidal transmission has already been described in U.S. Pat. No. 2,152,796 which was published in the year 1939. In said publication, two pairs of concave input and output discs are provided between which tiltably supported toroidal wheels are situated so that a torque transmitted, via an input shaft to the input discs, and the toroidal wheels, in accordance with the relative position of the toroidal wheels with a reduction ratio depending thereon, is fed in the form of a planetary gear to a summarizing transmission, via the output discs, a gear stage and a hollow shaft. The carrier of the planetary gear drives an output shaft, which is connected with the driving wheels, for example, of a motor vehicle. The output shaft is situated parallel to and spaced from the input shaft. The output gearwheel and both output discs are rotatably placed on a sleeve, which on its ends, is supported in bearing brackets. The arrangement of the bearing brackets, between each input and output discs, presupposes a sufficient large installation space between said discs.
The transmission, according to U.S. Pat. No. 3,739,658, likewise has a two-way variator with two input and output discs disposed in pair between, which tiltably mounted toroidal wheels, are situated. In this construction, a bearing bracket is horizontally disposed between the two output discs, which is part of the housing. The power from the output discs is supplied to a hollow shaft, via a planetary gear, which additionally acts as differential. The hollow shaft is non-rotatably connected with the output gear wheel and is rotatably retained by ball bearings in the bearing bracket.
The output gear wheel is in operative connection with a gear wheel which is non-rotatably fastened on the housing of a torque converter. The latter drives the output shaft of the transmission. The arrangement of the torque converter on the input of the output shaft requires a relatively large center distance between input and output shafts of the transmission. The applications for said transmission are thus very limited, since the required installation space is often not available.
U.S. Pat. No. 4,893,517 has disclosed a continuously variable toroidal transmission having one input shaft which penetrates a housing. The housing is divided by a partition wall in two hollow spaces in which are respectively supported one input disc and opposite to it one output disc with toroidal wheels therebetween, wherein the input disc and the output discs lie one in the hollow spaces on a common axis relative to which the wheels can be swivelled to obtain the desired speed ratio. The pairs of input discs and output discs are located in the hollow spaces with mirror symmetry, relative to each other, in a manner such that both output discs lie adjacent each other on opposite sides of the partition wall that separates the two hollow spaces from each other and in which a gear wheel is mounted which is driven by the two output discs.
The Applicants unpublished patent application DE 197 32 084.8 describes a continuously variable toroidal transmission in which the input shaft is surrounded by a torque shaft disposed coaxially thereto; the input shaft extends through the entire continuously variable transmission and is provided at its end with an axial disc. This axial disc is associated with a pressure device, which actuates a first input disc of a transmission unit in direction toward its associated output disc. The input disc of the second transmission unit supports itself, via an axial bearing on a second axial disc, and via a radial bearing on the input shaft.
Between the two transmission units is provided a cup-shaped bearing bracket element in which is located a gear wheel actuated by the two output discs of the two transmission units and meshing with an output gear wheel off an output shaft. The bearing bracket element forms, together with an upper and lower chassis bar, a supporting frame wherein the chassis bars support upper and lower cross yokes in which are mounted the supports for the toroidal wheels which can roll off on preselected, inclined planes in order thus to transmit in continuously variable ratio, the torque from the respective appertaining input disc to the appertaining output disc of the transmission unit.
The problem to be solved by the invention is to more compactly construct the variator and therewith the transmission and to increase the rigidity of the wheel supports and thus increase the stability of the variator.
The advantages attainable by the invention consist, among others, is that a more compact design is obtained as result of lower supports and, that the supports can be more rigidly designed, whereby displacements of contact point and less compensating movements due to warping is achieved. In addition, a tunnel compatibility is made possible, regarding a plurality of vehicles, due to the cross connection of the supports by means of the yokes, which appeared on the upper side in the former toroidal transmission, is eliminated.
The toroidal transmission, according to the invention, is advantageously designed both as a one-way and two-way toroidal transmission, the latter having two pairs of input and output discs. The transmission, according to the invention, likewise can be designed as one-way transmission with one input and one output shaft, but also as two-way transmission advantageously having one input shaft, one torque shaft disposed coaxially thereto and one output gear wheel between the two output discs.